Hydraulic control system

Abstract

A double-acting user has a first and an oppositely acting second pressure-fluid compartment. A source of pressure fluid receives fluid from a fluid reservoir. A first conduit has one section communicating with the first compartment of the user, and another section communicating with the source of pressure fluid. A second conduit communicates with the reservoir. A control valve is interposed in the first conduit and is movable between a first position in which it connects the sections of the first conduit with one another and a second position in which it connects both of the sections of the first conduit with the second conduit. A pressure-reducing and limiting valve has a first port communicating with the second compartment of the user, a second port communicating with the reservoir, a third port communicating with that section of the first conduit which in turn communicates with the source, and a pressure-limiting arrangement which serves to limit the fluid pressure in the second compartment of the user.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: 
     
       1. A hydraulic control system, comprising a double-acting user having a first and an oppositely acting second pressure-fluid compartment and a pressure responsive element therebetween and being arranged to move in a first direction counter to the urging of a load at one speed which is substantially uniform over the entire stroke length, and in a second direction with or without the urging of a load; a fluid reservoir; a source of pressure fluid communicating with said fluid reservoir; first conduit means having one section communicating with said first compartment, and another section communicating with said source; second conduit means communicating with said reservoir; and means for effecting movement of said element in said second direction without the urging of a load at another speed which is also substantially uniform over the entire stroke length, comprising control valve means interposed in said first conduit means and movable between a first position in which it connects said sections with one another, and a second position in which it connects said second conduit means with both of said sections, and pressure-reducing and pressure-limiting actuating valve means, including a first port communicating with said second compartment, a second port communicating with said reservoir, a third port communicating with said other section of said first conduit means, and pressure-limiting means operative for limiting the fluid pressure in said second compartment, said pressure limiting means comprises a valve member having a pressure responsive face directly and continuously open to said second compartment, said valve member being movable between one position in which it normally connects said third port with said first port, another position in which it connects said first port with said second port, and a further position in which it disconnects all of said ports from one another; and biasing means normally biasing said valve member to said one position. 
     
     
       2. A control system as defined in claim 1, wherein said control valve means is also movable to a third position in which it connects said second section of said first conduit means only with said second conduit means, to that pressure fluid from said source is recirculated to said reservoir. 
     
     
       3. A control system as defined in claim 1, wherein said biasing means comprises a spring dimensioned to yield and permit movement of said valve member from said one to said other position when the pressure in said second compartment exceeds a predetermined limit. 
     
     
       4. A control system as defined in claim 1, wherein said user comprises a cylinder and said element is a differential piston slidable in said cylinder and having a piston rod projecting from one end and extending through said cylinder, said first compartment being an annular compartment formed in said cylinder adjacent said one end of said piston by said piston and piston rod, and said second compartment being formed in said cylinder adjacent the other end of said piston. 
     
     
       5. A control system as defined in claim 1, wherein said user is connected with a load-lifting arm for raising and lowering the same. 
     
     
       6. A control system as defined in claim 1, wherein said third port communicates with said other section of said first conduit means in the region of said source. 
     
     
       7. A control system as defined in claim 1, wherein said source is a hydraulic pump. 
     
     
       8. A control system as defined in claim 1, wherein said control valve means comprises valve seats, and a valve member engageable with said valve seats in the respective positions of said control valve means. 
     
     
       9. A control system as defined in claim 1, wherein said control valve means disconnects in said first position said second conduit means from said sections.